# What exactly is anti-matter?

1. Dec 10, 2006

### Johnson

Probably a dumb question, but I have never had it explained to me.

I was just wondering if someone would be able to tell me what anti-matter is, from basics, how it is formed and how it interacts with normal matter.

-Johnson

2. Dec 11, 2006

### humanino

There are several approaches to define anti-matter. Mathematically, you could consider that an anti-electron (positron) is a negative-energy electron going back in time. This is a very convenient trick, but can be physically misleading. The flow backward in time is not physical, since it carries negative energy.

Take a look at those processes :

The two on the right are just propagation of a photon ($$\gamma$$) and electron $$e^-$$)
Let us concentrate on the diagram on the left. If time is flowing from left to right (and vertical represents space), what you see is an electron emiting a photon while it propagates. This is not a real process, one particle at least must be virtual, but this is no real concern here. The point is the following. If now you consider that the horizontal is space, and time flowing from bottom to top of the picture, the process now represent a (virtual) photon decaying into a pair positron/electron. The positron would in that case be the most-left red line, and the arrow indicates that this is a backward-in-time electron.

If you understand this, you are about to have understood how to create anti-matter, as well as how it interactes with ordinary matter